Hospitalization Linked to Clotting Risk in Pregnant Women

Norra MacReady

November 14, 2013

Pregnant women who enter the hospital for reasons unrelated to their pregnancy face a sharply increased risk for thromboembolism during their stay and several weeks thereafter, a new study suggests.

In a review of data on more than 200,000 women, hospital admission during pregnancy was associated with a 17.5-fold increase in the risk for venous thromboembolism (VTE) during the stay and a 6-fold increase in risk in the 4 weeks after discharge compared with pregnant women who did not require hospitalization.

Alyshah Abdul Sultan, a doctorate student from the Division of Epidemiology and Public Health, University of Nottingham, United Kingdom, and colleagues report their findings in an article published online November 7 in BMJ.

"The association between admission and [VTE] remained when we restricted our analysis to women without medical comorbidities including obesity, cardiac disease, and varicose veins," they write.

VTE is a prominent cause of maternal mortality in developed nations, the authors note. According to the American College of Obstetricians and Gynecologists, pregnant women have a 4-fold to 5-fold increased risk for thromboembolism compared with nonpregnant women. Nine percent of maternal deaths in the United States are caused by VTE, the college reports.

Despite these grim statistics, "there is a shortage of high quality evidence regarding which women are at greatest risk" for VTE, the authors write. In the general population, the risk for VTE during a hospital stay is more than 100 times greater than it is among outpatients. In this study, the authors tried to determine whether hospitalization is associated with a similar increase in risk among pregnant women.

The researchers analyzed data for women aged 15 to 44 years who became pregnant between 1997 and 2010, had at least 1 delivery resulting in a live birth, had no previous history of VTE, and were included in the Clinical Practice Research Datalink, a large database containing the primary care records of patients in the United Kingdom.

They identified 206,785 women who had 245,661 pregnancies during the study period. Of those pregnancies, 42,256 (17.2%) included at least 1 hospital stay, with 11,472 women admitted multiple times during 1 pregnancy, for a total of 59,537 periods of hospital admission.

The rate of VTE during the antepartum period (from conception to 2 days before childbirth) was 112/100,000 person-years. The rate outside pregnancy (excluding from 1 day before childbirth up to 12 weeks afterward) was 32/100,000 person-years. Gestational diabetes, cardiac disease, gestational acute systemic infection, hyperemesis, and varicose veins all were associated with an increased risk for VTE among pregnant women.

Hospital admission was associated with an absolute antenatal VTE rate of 1752/100,000 person-years during the hospital stay and 676/100,000 person-years after discharge. After adjustment for confounding factors including maternal age and calendar year, there was a 17.5-fold (95% confidence interval [CI], 7.69 - 40.0) increased risk for VTE during hospital admission and a 6-fold (95% CI, 3.74 - 10.5) increase in the 28 days after discharge compared with women who did not require admission.

Study limitations include questions about completeness of the data and diagnoses from participating centers, the relatively small number of VTE events during or immediately after hospital admission in the study population, and failure to account for the possibility that some patients may have been receiving thromboprophylaxis unbeknownst to the investigators.

The sedentary nature of hospital stays may help explain these findings, said Véronique Taché, MD, assistant clinical professor of obstetrics and gynecology, University of California, Davis, School of Medicine. "Any change that promotes immobility in a pregnant patient will place her at risk for a VTE," she told Medscape Medical News. "A hospital admission is one such change, but other situations such as a car ride or a plane ride also [increase] the risk of VTE."

Also, "you may have an intravenous line in, you may have a long time with nothing to eat or drink, so there may be periods of dehydration," which can increase VTE risk, said Maryam Tarsa, MD, associate clinical professor of reproductive medicine at the University of California, San Diego, School of Medicine. "You might be undergoing surgery or certain studies, so you're more prone to procedures, so [the risk for VTE] might be an effect of what is being done to you. In our pregnant population, we always emphasize the importance of mobilization and hydration to decrease the risk of thromboembolism."

When it comes to reducing the risk for VTE, "I hesitate to recommend pharmacologic thromboprophylaxis since other mechanisms, such as sequential compression devices [SCDs] or compression stockings can help reduce the risk of VTE without the risk associated with pharmacologic treatments," Dr. Taché said. In the United States, use of agents such as low–molecular weight heparin in pregnant women usually is reserved for patients who are at extremely high risk for VTE or have thrombophilias.

The authors did not address the management of inpatient antepartum patients in the United Kingdom, Dr. Taché added. "Are SCD routinely used, do patients have the option of walking around, can they see a physical therapist and do exercises in bed? If patients do all this and still have VTE, then the push for pharmacological thromboprophylaxis might be justified."

One study author has received honorariums for lectures from Leo Pharma and sanofi-aventis (makers of tinzaparin and enoxaparin and the low–molecular weight heparins used in obstetric thromboprophylaxis) and has received payment from Leo Pharma for development of an educational slide kit about obstetric thromboprophylaxis. The other authors, Dr. Taché, and Dr. Tarsa have disclosed no relevant financial relationships.

BMJ. 2013;347:16099. Full text

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